Time Jump

I'm looking for a specific type of time jump manga where he main character either goes forward or backward in his/her own life, but keeps the same maturity. A standard layout is where maybe there's some type of accident, and the mc wakes up in her 5-year-old body and maybe has to relive her life. I really want the mc to keep his/her intelligence, (maybe) memories, and maturity.

Two examples: where an adult has to relive her high school days, there's The Country is Saved!. Not excellent because she's a little foolish (and therefore doesn't seem grown-up enough to me; her high-school self blends in with the other high schoolers). On the other side, the second oneshot in Itou-san is a case where

Spoiler (mouse over to view)

the mc's boyfriend is a child who skipped ahead in life to become an adult.

Bonus points if history/the future is somehow changed because of this reliving. That would be awesome.

Another one that meets your criteria is Mujaki no Rakuen. An incident after the MC's class reunion sends him back to 5th grade (whatever that means). It should be noted that, first, this manga is practically a H manga. And secondly, I personally disliked it.

I meant in the sense that her soul/memories were swapped into a new body. I used the term "body swap" since it has a more immediate connotation than "reincarnation/past lives", which more often involves centuries-long time skips.

Heptagon - Female lead (24) goes back to when she was a teenager (14), which she discovers to be a more decisive time in her life than she thought. Highly recommended read.

Nam Gi-han to Be an Elite - 24 year old dude returns to his 11 year old self. It's kind of gag-like. I don't like how everything he does turns out to be futile for the sake of humor. (That isn't really a spoiler since about 3-4 chapters in, you realize this pattern.)